Question about external Hard drives

I bought my computer a long long time ago but I've replaced everything except for the hard drive so all I have is 30 Gigs of HD space, Right now I have about 2 left and I want to download something that takes up 4. So I was wondering if I can buy an external hard drive and have it plugged in all the time. Could I download the game onto the external one and play it on my computer if the external hard drives plugged in. Or can I transfer all my music onto the external one and still listen to it without transferring it all back.

sorry about the long question but I cant explain it any other way.

if you have had it a long time (30 gig says a very long time) you probably have the earlier version of USB which is slow.

instead of spending on an external you could buy a second internal hard drive and transfer everything over to it for safety.

i am assuming that your drive being old is not too much longer for this world and i would bet you have not been making regular backups of the things that are of value to you on it.

one failed drive where i lost everything tought me to have 2 drives and do backups

some local stores will install a drive bought there for free or a small charge

good luck

thanks for the help